I have an S&W M&P lower I would like to put a lightweight upper on.  I prefer a 1:8 or 1:9 twist to shoot 45gr and 55gr ammo.  The primary use of the gun will be for small game hunting and plinking.  I will probably put a red dot or low power scope on.  At 63 the iron sights are hard to use.

Also, I have a HBAR scoped upper on the lower now and is great for target shooting and still hunting.

thanks

Bushmaster's Superlite has a very accurate barrel.  Not sure if you can purchase just the upper but it's worth looking for.